Need help on fluid therapy

first look at one of the indications for an iv:

1. to establish or maintain a "fluid balance" or "electrolyte balance"

then look at the primary functions of sodium (the 0.9%ns of the iv solution)

1. to chemically maintain osmotic pressure

2. acid base balance

3. to transmit nerve impulses

then look at the primary functions of potassium

1. electrical activity of the heart

2. acid base balance

3. nerve conduction

whether a crystalloid fluid is isotonic, hypotonic, or hypertonic is based on the amount of sodium (salt) or glucose (dextrose-sugar) that is dissolved in the fluid (or how weak [0.45%ns] or strong [3%-5%ns] of a "tonic" the solution is).

if you add a hypotonic solution (0.45%ns) or (more water with a reduced amount of salt) to the blood vessels then the body wants to maintain homeostasis and the higher salt content outside the blood vessels pulls water from the blood vessels to bring the sodium in the vessels back into balance.

when i say homeostasis of the blood here i am speaking of the normal amount of sodium dissolved in our blood that closely matches 0.9% normal saline iv solution.

if you add an isotonic solution (0.9%ns) to the blood vessels then that closely matches the tonicity (or moles, molecules, or particals of sodium) already in the blood vessels, therefore no water needs to be shifted in the body compartments to bring the blood back to homeostasis.

if you add a hypertonic solution (3%-5%ns) or (excess salt) to the blood the body wants to get back to homeostasis and it pulls more water into the blood to dilute the salt.

for short tonicity is aboutthe amount of particals dissolved in a solution and how this works to move water within the body compartments.

you asked: "i know that 0.9% normal saline is an isotonic solution but if 20meq of kcl is added is it considered isotonic or hypotonic?"

in all my reading about iv fluids and their tonicity i have not seen iv fluid with kcl listed for it's tonicity. however i have seen it discussed that potassium is an additive.

for 0.9% ns with 20meq of kcl. the 0.9% ns makes this an isotonic solution remember that one of sodiums primary functions is to maintain osmotic pressure. the 20 meq of kcl is an additive to provide necessary potassium. remember potassiums primary functions are for the electrical activity of the heart, acid base balance and nerve conduction.the potassium is not functioning to maintain osmotic pressure so it should not change the tonicity of the fluid it is added to.

maybe think of it like piggy backing a medicine with an iv fluid. it does not change the tonicity of the fluid being administered.